1. Technical Field
One or more embodiments of the present invention relates to semiconductor devices and microphones. Specifically, one or more embodiments of the present invention relate to a semiconductor device in which a semiconductor element is accommodated in a package. One or more embodiments of the present invention also relates to a microphone in which a microphone chip (acoustic sensor) is accommodated in a package.
2. Related Art
A microphone manufactured using the MEMS (Micro Electro-Mechanical Systems) technique generally has a structure in which an MEMS microphone chip is accommodated in a package configured by a substrate and a cover. The microphone includes that in which the microphone chip is mounted on the cover and that in which the microphone chip is mounted on the substrate. An acoustic hole for introducing the acoustic vibration into the package may be opened in the cover or may be opened in the substrate.
The microphone has a characteristic in that the sensitivity becomes higher as the capacity of the back chamber (space on the side opposite to the acoustic hole with respect to the diaphragm) becomes larger. Thus, if the acoustic hole is formed in the cover, the microphone chip may be mounted on the inner surface of the cover so as to cover the acoustic hole in terms of increasing the sensitivity of the microphone.
If the acoustic hole is formed in the substrate, the capacity of the back chamber can be increased by mounting the microphone chip on the substrate so as to cover the acoustic hole. However, if the microphone chip is mounted on the substrate so as to cover the acoustic hole of the substrate, drawbacks such as contamination of the microphone chip, sticking of the microphone chip to the diaphragm, and the like may occur due to the soldering fume that occurs when mounting the substrate of the micro-phone to the circuit substrate of the device. The microphone chip is thus sometimes mounted on the cover even if the acoustic hole is formed in the substrate.
The microphone in which the microphone chip is mounted on the cover is disclosed in US 2008/0283988 A1. FIG. 1 is a cross-sectional view of a microphone disclosed in US 2008/0283988 A1. In a microphone 11 described in US 2008/0283988 A1, a microphone chip 13 (MEMS microphone) and an IC chip 14 are mounted in a recess provided in a cover 12. The microphone chip 13 is arranged to cover an acoustic hole 20 formed in the cover 12. An input/output wiring 17, which is a signal input/output unit, is formed on the substrate 16, and a connection electrode 18 electrically conducted with the input/output wiring 17 is arranged on the upper surface of the substrate 16. The cover 12 is fixed to the upper surface of the substrate 16, and the microphone chip 13 and the IC chip 14 are accommodated in a package including the cover 12 and the substrate 16.
In such microphone 11, the microphone chip 13 and the IC chip 14 are connected by a bonding wire 15a. A plurality of internal conductor wirings 19 is arranged on the inner surface of the cover 12 from the upper surface (top surface) to the lower end at the side surface, where the microphone chip 13 is connected to a bonding pad 19a at the end of the internal conductor wiring 19 by a bonding wire 15b and the IC chip 14 is also connected to the bonding pad 19a at the end of the internal conductor wiring 19 by a bonding wire 15c. The microphone chip 13 and the IC chip 14 are electrically conducted to the input/output wiring 17 by contacting each internal conductor wiring 19 to the connection electrode 18 of the substrate 16 when attaching the cover 12 to the upper surface of the substrate 16.
However, in the microphone 11 of US 2008/0283988 A1, the internal conductor wiring 19 needs to be arranged in the recess from the upper surface thereof to the lower end at the side surface, and hence the processing of the internal conductor wiring 19 is troublesome. When mounting the microphone chip to the cover such as in the above case, the wiring for connecting the microphone chip to the substrate becomes complex, the manufacturing cost of the microphone becomes high, and the reliability lowers.
In the structure of the microphone 11, wire bonding needs to be carried out on the bonding pad 19a within the recess depressed to a box shape of the cover 12, and hence a space for the jig (capillary) for wire bonding to enter is required at the edge of the recess. A redundant space is thus necessary in the recess, which enlarges the package.
In a microphone 21 (condenser microphone) disclosed in US 2007/0058826 A1, the package is divided into three members, a cover 22, a side substrate 29, and a substrate 28. A microphone chip 23 (microphone element) and an IC chip 24 are mounted on the cover 22, and the microphone chip 23 is arranged to cover an acoustic hole 22a of the cover 22. The microphone chip 23 and the IC chip 24 are connected by a bonding wire 26a, and a bonding pad 25 arranged on the cover 22 and the microphone chip 23, and the IC chip 24 are electrically connected by bonding wires 26b, 26c, respectively. An external connection terminal 27, which is a signal input/output unit, is arranged on the upper surface of the substrate 28, a connection electrode 33 is arranged on the lower surface of the substrate 28, and the external connection terminal 27 and the connection electrode 33 are connected by a through-hole 32. The periphery of a space between the cover 22 and the substrate 28 is surrounded by the side substrate 29. The side substrate 29 is sandwiched between the cover 22 and the substrate 28, and an upper end and a lower end of the through-hole 30 and a coil spring 31 are respectively pressure welded to the connection electrode 33 and the bonding pad 25 to electrically conduct the bonding pad 25 to the external connection terminal 27.
In the microphone 21 having such structure, the microphone chip 23 and the IC chip 24 are mounted on the cover 22, the microphone chip 23 and the IC chip 24 are wire bonded to the bonding pad 25, and then the side substrate 29 and the substrate 28 are overlapped on the cover 22 to electrically conduct the bonding pad 25 and the external connection terminal 27. Therefore, the wire bonding work can be easily carried out without being inhibited by the side substrate 29, and the space inside the package can be made small.
In the structure described in US 2007/0058826 A1, however, the number of members configuring the package increases, and the package structure becomes complex and the cost of the microphone 21 becomes high as the structure of the through-hole 30 and the coil spring 31 need to be formed in the side substrate 29. Furthermore, the outer size of the package cannot be reduced because the wall thickness of the side substrate 29 cannot be reduced even if the space in the package does not become large.